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Geographic Distribution

Where malaria is found depends mainly on climatic factors such as temperature, humidity, and rainfalls. Malaria is transmitted in tropical and subtropical areas, where:

• Anopheles mosquitoes can survive and multiply
• Malaria parasites can complete their growth cycle in the mosquitoes ("extrinsic incubation period").

Temperature is particularly critical. For example, at temperatures below 20°C (68°F), Plasmodium falciparum (which causes severe malaria) cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted.

Geographic Distribution of Malaria

Even within tropical and subtropical areas, transmission will not occur:

• At high altitudes
• During cooler seasons in some areas
• In deserts (excluding the oases)
• In some islands in the Pacific Ocean, which have no local Anopheles species capable of transmitting malaria
• In some countries where transmission has been interrupted through successful eradication.

Generally, in warmer regions closer to the equator:

• Transmission will be more intense
• Malaria is transmitted year-round
• P. falciparum predominates.

The highest transmission is found in Africa South of the Sahara.

In cooler regions, transmission will be less intense and more seasonal. There, P. vivax might be more prevalent because it is more tolerant of lower ambient temperatures.

In many temperate areas, such as western Europe and the United States, economic development and public health measures have succeeded in eliminating malaria. However, most of these areas have Anopheles mosquitoes that can transmit malaria, and reintroduction of the disease is a constant risk.

Travelers planning a visit to areas with potential malaria risk can consult the destinations pages on the Travelers' Health site.